Reforming of hydrocarbons



2 sheets-sheet 1 Filed Oct. 27. 1950 NIJ Nav. 16, 1954 D. D. MaCLARENREFORMING OF HYDROCARBONS 2 Sheets-Sheet 2 Filed 001,. 27. 1950 mnzm ImiDonald 3D. modcwen.

@Trb/nbc? 235 Clbborne REroRMlNG oF HrDRocARBoNs Donald D. MacLaren,Plainfield, N. J., assignor to Standard Oil Development Company, acorporation of Delaware Application October 27, 1950, Serial No. 192,417

12 Claims. (Cl. 1915-50) This invention relates to the reforming ofnaphtha in the presence of a catalyst which circulates in a continuousmanner through the reforming zone and pertains more particularly to amethod and apparatus for removing hydrocarbons and gas entrained in thecatalyst withdrawn from the reforming zone. The invention findsparticular application to hydroforming processes in which light gas richin hydrogen produced during the reforming process is recycled to thereforming zone.

It has heretofore been proposed to reform naphtha fractions in thepresence of a recycled tail gas containing from 40 to 70 or more percentof free hydrogen but under such conditions that there is no netconsumption of hydrogen during the treatment. This process is commonlyknown as hydroforming This term, as used hereinafter, refers to acatalytic operation carried out in the presence of a reformnig catalystsuch as a sixth group metal oxide supported on active alumina and in thepresence of hydrogen, the principal chemical reaction involving thedehydrogenation of hydrocarbons accompanied by certain side reactions,such as isomerization, cyclization, cracking, polymerization, etc.

The present invention is particularly applicable to what is known as theuid hydroforming process wherein finely divided catalyst maintained influid condition by admixture with gas is continuously circulated througha hydroformng zone and thereafter through a heating or regenerationzone. In the heating and regeneration zones the catalyst is heated bythe combustion of carbonaceous deposits to a temperature substantiallyhigher than that maintained in the reaction zone. When carrying out theprocess in this manner substantially all the heat required can besupplied by hot regenerated catalyst circulated at a relatively rapidrate from the regenerator to the reactor. It is particularly importantin this type of operation to treat the spent catalyst with a strippingor purging gas prior to regeneration to recover valuable products,particularly hydrocarbons adsorbed on or associated with the catalystwithdrawn from the reactor under relatively high pressures and also toavoid burning of such products in the regenerator with a resultantundesirable inf crease in the amount of heat liberated therein withoutan equivalent increase in the removal of carbonaceous deposits from thecatalyst.

It has previously been proposed to treat the catalyst withdrawn from thereforming zone with .a portion of the tail gas from the process to avoiddiluting the reaction products with extraneous gas. This practice,however, results in the transfer of a substantial amount of hydrogen andlight hydrocarbons (C1-C5) to the regenerator Where they are burnedalong with the carbon deposits formed on the catalyst during thereforming treatment. This not only reduces the carbon burning capacityof the regenerator but uses up a substantial amount of hydrogen. 'I'helatter may, n turn, reduce the hydrogen content of the recycle gasreturned to the reactor to a point Where the recycle gas must beenriched with hydrogen.

It has also been proposed to strip the catalyst withdrawn from thereforming zone with steam but it has been found that steam has anadverse effect on the activity of the catalyst. The use of inertstripping gases, such as ilue gas, nitrogen, etc. is, therefore,desirable and has been suggested heretofore. However, prior art systemsproviding for the use of inert stripping gases of this type involveserious drawbacks. Recovery of the Valuable hydrocarbons removed fromthe catalyst by the :a itcd States Patent O 2,694,672 Patented Nov. 16,1954 ICC stripping gases is indispensable economically in commercialoperation. Most of the known processes combine the stripping zone efuentwith the eflluent of the hydroforming zone so as to utilize the mainproduct recovery system for the recovery of the stripped hydrocarbons.However, this type of operation causes an undue dilution of the reactorrecycle gas with the inert stripping gas which cannot be separated fromthe recycle gas by conmiercially practical means. This dilution soconsiderably reduces the hydrogen concentration of the recycle gas thatsubstantial proportions of extraneous hydrogen must be supplied to therecycle gas to maintain the same at the desired 40-70% hydrogenconcentration. It has, therefore, been suggested either to provideseparate hydrocarbon recovery equipment for the stripping zone etliuentor to use the latter as a fuel. Either procedure involves obviousdisadvantages for the economics of the process. The present inventionovercomes this diliculty.

It is, therefore, the principal object of the present invention toprovide improved means permitting the use of inert stripping gases in auid type catalytic hydroforming process with full recovery of thestripped hydrocarbons and without dilution of the recycle gas streamwith inert stripping gases.

Other objects and advantages will appear from the description of theinvention given below wherein reference will be made to the accompanyingdrawing in which Figure l is a semi-diagrammatic illustration of asystem adapted to carry out an embodiment of the invention; and

Figure 2 is a similar illustration of a portion of the system of Figurel modiiied to carry out another embodiment of the invention.

In accordance with the present invention, the catalyst withdrawn fromthe hydroforming zone is passed to a separate stripping zone andstripped therein with an inert, essentially non-combustible gas such asue gas, nitrogen, etc., preferably in the uidized state. The gasiformefuent of the stripping zone is combined with the main product gasstream from which normally liquid products have been previously removedby condensation, the stripper effluent entering this product gas streamat a point subsequent to the withdrawal therefrom of the recycle gasstream but prior to the entry of the main product gas stream into theequipment normally provided for the recovery of light ends. When sooperating, inert gases may be used for stripping Without diluting therecycle gas stream and without the requirement of additional recoveryequipment for a complete recovery of the hydrocarbons stripped off thecatalyst.

In accordance with the preferred embodiment of the invention, the spentcatalyst is subjected to a two stage stripping treatment. In a firststripping stage the catalyst used in the hydroforming reaction isstripped with a portion of the recycle gas streams to remove theheaviest hydrocarbons adhering to the catalyst. The gasiform eluent fromthis stage may be combined with the main product stream at any desiredpoint prior to liquid product recovery. Conventional internal strippingmeans arranged within, and discharging their gaseous effluent into thehydroforming zone may be used in this stage. In the sceond strippingstage, the catalyst freed of relatively heavy hydrocarbons in the firststage is further stripped with inert gas to remove adhering light endsand hydrogen entrained in the first stripping stage. The gaseous eluentfrom this second stage is passed to the main product gas stream fromwhich the recycle stream has been previously branched olf and themixture is supplied to conventional light ends recovery equipment.V Thecatalyst so treated is free of valuable entrained materials, such ashydrocarbons and hydrogen, and may be passed on to the regeneration zonefor reheating and burning of its carbonaceous deposits in any mannerknown per se.

The process of the invention may be carried out at any elevated pressuresuitable for hydroforming without requiring additional equipment forpressure control. In some cases, it may be desirable to increase thehydrogen concentration of the recycle gas by reducing its hydrocarboncontent for which purpose the pressure on the liquid product recoverysystem may be increased. The process of the invention may be readilyadapted to this type of operation by merely providing an additionalpressure control valve -betweenthe inert gas stripper and the point oflentry vof its effluent into the product gas stream. The invention mayalso be applied to ysingle stage stripping with inert gas, in which casesuitable equipment may be provided for the recovery of relatively heavyhydrocarbons from the stripper effluent.

From the `foregoing it will be appreciated that the present inventionpermits the use of inert stripping gases to remove valuable combustiblesfrom the hydroforming catalyst to be regenerated, without thedisadvantages inherent in conventional operation, which means that theinvention has made possible for the first time the use of inertstripping gases in commercial fluid type hydroforming operations. Thesignificance of this development becomes apparent from a comparison ofrecycle gas with inert gas as the stripping medium.

As indicated above, entrainment of the hydrogen-rich stripping gas fromthe reactor stripper to the regenerator is particularly significant inhigh pressure, high circulation rate iluid hydroforming operations. Theinagnitude of this entrainment is shown by the experimental datatabulated below illustrating the effect on product yields at about 950F., 200 p. s. i. g. pressure and at a fluidized catalyst to oil weightratio of 6 corresponding to 0.4 hr. catalyst residence time when usingreactor recycle gas as compared to equivalent proportions of inert gasas the stripping medium, under otherwise substantially equal conditions.

It will be noted that at these conditions the effect of inert gasstripping is not only to reduce regeneration load by eliminating theburning of hydrocarbons and hydrogen (1.1 wt. per cent coke equivalentof hydrocarbons and 130 s. c. f./bbl. hydrogen, respectively), but alsoto iricrease the gasoline yield (0.4 volume per cent) because of the C4and heavier hydrocarbons carried over to the regenerator in the case ofrecycle gas stripping. Thus, effective stripping with inert gas as it ismade possible by the present invention is seen to be extremelyimportant.

Having set forth its object and general nature, the invention will bebest understood from the subsequent more detailed description ofspecific embodiments illustrated in the drawing. Referring now to Figure1, the system shown therein essentially comprises a hydroforming reactor15, a catalyst regenerator 78 and a catalyst stripper 62, the functionand coaction of which will be presently described.

In operation, a naphtha feed of, say about 200 to 430 F. boiling range,which may contain about 3050% of naphthenes is supplied to the systemthrough line 1 and may be passed through a tired coil 3 to be vaporizedand heated therein to temperatures of about 500*l000 F. The preheatedvapors leave coil 3 at a pressure of about 100-500 p. s. i. g. via line5 which receives from line 7 a gas rich in hydrogen, consistingessentially of recycle gas and containing about 4070% of hydrogen, theremainder being low molecular weight hydrocarbons of 1 4 carbon atomsper molecule. This gas, obtained as will appear hereinafter, ispreheated in fired coil 9 so as to enter line at a temperature of about900-l000 F., and in amounts of about 50G-5,000, preferably aboutLOGO-3,000, standard cubic feet of gas per barrel of naphtha feed.

The mixture of naphtha vapors and gas owing through line 5 is suppliedvia standpipe 11 with regenerated and stripped hot subdividedhydroforming catalyst which may have a fluidizable average particle sizeof about 40-80 microns and a temperature of about 950-l250 F. as aresult of the regenerating treatment to be described later on. Thecatalyst may be any one of those known to catalyze the hydroformingreaction, such as oxides of molybdenum, chromium or tungsten on acarrier such as activated alumina, zinc aluminate spinel and the like,preferably molybdenum oxide on activated alumina; it may be added toline 5 in amounts of about 0.5 to 7 lbs. of catalyst per lb. of naphthafed. A dilute suspension of catalyst in vapors and gases is formed inline 5 and passed at a reaction temperature of preferably about 900l000F. to a lower portion of a conical feeding device 13 arranged in theconical bottorn portion of a substantially cylindrical hydroformingreactor 15 designed for fluid solids operation. As shown in the drawing,a free space S is provided between the walls of feeding device 13 andthose of reactor 15 for stripping purposes as will appear more clearlyhereinafter. Reactor 15 is so dimensioned that at the prevailing flowconditions a relatively dense highly turbulent mass M15 forms therein,uidized by the upowing gases and vapors to resemble a boiling liquidseparated by an interface or level L15 from an overlying dilute phaseD15. Linear superficial vapor velocities of about 0.3-3 ft. per secondare normally suitable for this purpose. Reaction conditions in reactor15 may include temperatures of about 900 1000 F., pressures of aboutl00-500 p. s. i. g. and vapor-solids contact times corresponding to aspace velocity of about 0.1 to 1.0 lbs. of oil per hour per lb. ofcatalyst.

Reaction vapors and gases containing some entrained catalyst areWithdrawn overhead from level Lis and may be passed through conventionalgas-solids separation means, such as cyclone separator 17, from whichseparated catalyst may be returned to mass M15 via line 19. The gasiformefuerit now substantially free of entrained solids is passed throughline 23 to a cooler or condenser 25 wherein it is cooled tosubstantially room temperature and most of the normally liquid productsare condensed. The cooled efiiuent then may be passed via line 27 to agas-liquid separator 29 from which liquid hydroformate may be recoveredvia line 31 and passed to suitable workup equipment includingfractionation and filtration equipment to remove entrained solids, etc.(not shown).

The gasiform overhead from separator 29 containing about 40-70% ofhydrogen and 30-60% oflow molecular weight hydrocarbons may be withdrawnvia line 33. The portion of the gas not required for recycle may bepassed via line 3S directly to light ends recovery system 40, if desiredafter pressure release through pressure control valve 37. System 40 maycomprise conventional liquid absorption and/or solid adsorptionfacilities, etc. Tail gas consisting essentially of Ci-Ca hydrocarbons,hydrogen and inert stripping gas introduced as will appear later on, maybe vented or passed to any suitable use via line 42. Light hydrocarbons,mainly Cs-Cs compounds may be recovered via line 44.

The remainder of the gasiform eflluent in line 33, which is not passedto line 3S is fed to line 46 to be circulated by pump 4S as recycle gas.Most of this recycle gas is passed via line and 52 to preheater 9 andline 7 to supply hydrogen to the process as described above. lf desired,fresh hydrogen may be supplied to the system via line 54. A proportionof the recycle gas in line 46, amounting to about 20 to 300 c. f. ofrecycle gas at stripper conditions per 1000 lbs. of catalyst may bebranched off through line 56 and supplied through one or more lines 5Sto space S of reactor 15 forstripping purposes, preferably afterreheating to about 800 to l000 F. in heat exchange with hot reactor yorregenerator effluent in any conventional manner (not illustrated).Subdivided catalyst from mass M15 drops continuously into space Swherein it is stripped and maintained in a dense readily yflowing stateby the stripping gas suppliedthrough lines 58, stripping gas andstripped vapors entering reactor 15 to be withdrawn together with thereaction products as described above.

Catalyst which is substantially free of relatively high boilinghydrocarbons, but which contains carbonaceous materials deposited in thecourse of the reaction as well as .hydrogen and light hydrocarbonsentrained from the stripping gas in space S, is withdrawn under thepseudohydrostatic pressure of mass M15 via line 60 substantially at therate at which catalyst is supplied via line 5 to reactor 15. Line 60,which may have the form of a conventional standppe aerated and furtherstripped through one or more taps t with small amounts of recycle gas orthe like. feeds into a separate stripper .62 which has the form of avertical substantially cylindrical vessel provided in its bottom portionwith a gas distributing means, such as a perforated plate or grid 64. Aninert gas. such as ue gas` nitrogen or the like, at temperatures in therange of about 400 to 1000 F. is supplied from line 66 through grid 64to the lower portion of stripper 62 in amounts of about 20 to 300 c. f.at stripping conditions per 1000 lbs. of catalyst circulated.

AStripper 62 is so dimensioned that, at the ilow conditions indicated, afluidized mass M62 having an upper level L62 is formed in stripper 62substantially as described with reference to mass M of reactor 1S. Atthese conditions the catalyst in stripper 62 may be substantiallycompletely freed of adhering or occluded hydrocarbons and hydrogenwithin residence times which need not substantially exceed about minutesand which normally may be maintained within the approximate rangeof-1-20 minutes. A mixture of stripping gas and stripped constituentspasses upwardly from level L62 through gassolids separation means, suchas cyclone 68 from which separated catalyst may be returned via dip-pipe70 to mass M62. The gaseous stripper eiuent now substantially free ofentrained solids is passed via line 72 to line to be mixed therein withthe gasiform effluent of separator 29 at a point downstream of therecycle gas take-off line 46. In this manner, the hydrocarbon content ofthe stripper efuent may be recovered in light ends recovery systemtogether with light product hydrocarbons from line 33 without dilutionof the recycle gas stream in line 46 with inert stripping gas.

Returning now to stripper 62, the catalyst stripped of volatilecombustibles may be withdrawn at a temperature of about 800-1000 F.under the pseudohydrostatic pressure of mass Mez via standpipe or thelike 74 and suspended in line 76 in air supplied to line 76 atatmospheric temperature. Additional air to establish amounts sucient toburn oi most of the carbonaceous deposits and adsorbed hydrogen, and toaccount for the normal oxidation reduction cycle of the catalyst isadded via line 77. About 1 to 15 c. f. of air per lb. of catalystcirculated is normally sufficient for this purpose. The catalystin-airsuspension so formed is passed to the conical bottom of regenerator 78provided with distributing means, such as grid plate 80. Regenerator 78is so designed that a tluidized mass Mrs basing a level L78 is formedtherein in a manner similar to that described with reference to massesM15 and Mez. Suiicient catalyst residence time is provided inregenerator 78 for the desired degree of combustion and to reheat thecatalyst to about 950-l250 F. Flue gases containing entrained solids arelwithdrawn through line 81 via cyclone 82 from which separated catalystmay be returned to mass M18 via dip-pipe 84 or discarded via line 86.The hot llue gases may be used as stripping medium in stripper 62 and topreheat process uids in any conventional manner. Make-up catalyst may besupplied together with the naphtha feed in any conventional manner.

Regenerated catalyst is withdrawn substantially at the temperature andunder the pseudohydrostatic pressure of mass Mrs through standpipe 11 tobe supplied to line 5 as described above. Small amounts of a strippingmedium, such as recycle gas or product tail gas, are supplied tostandpipe 11 via one or more taps t to aerate the solids and displaceoccluded air and flue gas therefrom.

As pointed out above, in certain fluid hydroforming operations where theamount of hydrogen produced is not sufficient to maintain the hydrogenconcentration of the recycle gas at the desired value, some form ofenriching system may be added to increase the hydrogen concentration byremoving more of the heavier hydrocarbons from the overhead vaporstream. The present invention may be used in a system of this nature, asshown in Figure 2 in a simplified manner. Figure 2 shows chieflyportions of the product recovery system used in combination with theprocess of the invention, most of the elements common to the systems ofFigures 1 and 2 and not essential for a proper understanding of Figure 2having been omitted for the sake of simplicity. Such common elements asappear in both figures have been identified by like reference numerals.

Referring now to Figure 2, the product eluent from reactor 15 passingthrough lines 23 and 27 and condenser 25 to separator 29 is treated inthe latter substantially at the pressure of reactor 15 as described withreference to Figure 1. However, the gasiform euent in line 33 'and 6 aportion, say about 20 to 70%, of the liquid products in line 31 arecompressed in pressure boosters 90 and 92, respectively, to a pressureof about 200 to 500 p. s. i. g. and passed via cooler 94 to a highpressure separator 96 maintained at a temperature of about 60 to 100 F.Additional liquid product may be recovered via line 98 while gasiformetlluent is passed via lines 100 and 35 provided with pressure controlvalve 37 to the lightends recovery system 40 of Figure l. The recyclegas stream which is branched off line 100 via line 46 at a pointupstream of control valve 37 is now substantially leaner in hydrocarbonsand accordingly richer in H2 as compared with the recycle stream ofFigure 1. The gaseous eluent of stripper 62 is withdrawn via line 72which is now provided with a pressure control valve 102 because reactor15 and stripper 62 may be at a pressure dilerent from that in line 100.For the same reason, line 72 now feeds into line 35 at a pointdownstream of control valve 37. ln all other respects, operation of thesystem of Figure 2 is identical with that of Figure 1 described above.

Both systems illustrated in the drawing may be operated without the rststage internal stripper S described above. In this case, system 40 willpreferably contain v suitable equipment for the recovery of relativelyhigh boiling hydrocarbons, such as suitable condensers, gasliquidseparators, absorbers, etc. Other modification of the system illustratedwill appear to those skilled in the art without deviating from thespirit of the invention.

The above description and exemplary operations have served to illustratespecific embodiments of the invention but are not intended to be limitedin scope.

What is claimed is:

1. In the process of continuously hydroforming naphthas in the presenceof a uidized hydroforming catalyst circulating between a fluid-typehydroforming zone and a iluid type catalyst regeneration zone for thecombustion of carbon on the catalyst, wherein the product efuent of saidhydroforming zone is separated into normally liquid products and a gasstream, a substantial portion of said gas stream is branched off andrecycled to said hydroforming zone and the remaining tail-gas portion ofsaid gas stream is supplied to a light ends recovery zone, theimprovement which comprises stripping said catalyst circulating fromsaid hydroforming zone to said regenerating zone in a separate strippingzone with an inert essentially non-combustible stripping gas selectedfrom the group consisting of ue gas and nitrogen to remove volatile andgaseous combustibles from said catalyst prior to its entry into saidregeneration zone, withdrawing a mixture of said inert stripping gas andvolatile combustibles from said stripping zone and adding said mixtureto said tail-gas stream at a point subsequent to the branching-oil' kofsaid recycled gas portion and prior to said light ends recovery zone,whereby said recycled gas stream and said hydroforming zone are keptentirely free of said inert stripping gas.

2. The process of claim 1 in which said inert gas comprises ue gas.

3. The process of claim 1 in which said inert gas comprises nitrogen.

4. The process of claim l in which said catalyst is maintained in saidstripping zone in the form of a dense turbulent solids mass iluidized bysaid inert gas.

5. The process of claim 1 in which said hydroforming zone is maintainedat a pressure of about 100-500 p. s. i. g. and said catalyst iscirculated between said hydroforming and regeneration zones at arelatively high rate within the range of about 0.5-7 lbs. of catalystper lb. of naphtha fed to said hydroforming zone.

6. In the process of continuously hydroforming naphthas in the presenceof a uidized hydroforming catalyst circulating between a fluid-typehydroforming zone and a fluid-type catalyst regeneration zone for thecombustion of carbon on the catalyst, wherein the product eflluent ofsaid hydroforming zone is separated into normally liquid products and agas stream, a substantial portion of said gas stream is branched olf andrecycled to said hydroforming zone and the remaining tail-gas portion ofsaid gas stream is supplied to a light ends recovery zone, theimprovement which comprises stripping the catalyst withdrawn from saidhydroforming zone in a rst stripping zone with a portion of saidbranched-01T recycle gas to remove relatively high boiling volatilecombustibles from said-catalyst, further strippingy said strippedcatalyst in av separate. second stripping zone with an inert essentiallynon-combustible` stripping gas selected from the group consisting of uegas and nitrogen to remove relatively low boiling and gaseouscombustibles including combustible constituents of said recyclestripping gas from said catalyst prior to its entry into saidregeneration zone, withdrawing a mixture of said inert stripping gas andremoved gaseous combustibles from said second stripping zone and addingsaid mixture to said tail-gas stream at. a point subsequent to thebranching-off of said recycle gas stream and prior to said light ends`recovery zone,v whereby said recycled gas stream and said hydroformingzone are kept entirely free of said inert stripping gas.

7. The process of claim 6 in which a mixture of recycle stripping gasand relatively high boiling combustibles is withdrawn from said firststripping zone and said last-named mixture is combined with said producteliuent prior to said separating into normally liquid products and a gasstream.

8. The process of claim 6 in which said catalyst is maintained in saidsecond stripping zone in the form of a dense turbulent mass fluidized bysaid inert gas.

9. In the process of continuously hydroforming naphthas at elevatedhydroforming temperatures and pressures in the presence of iiuidizedhydroforming catalyst circulating between a uid-type hydroforming zoneand a iiuid type catalyst` regeneration zone for the combustion ofcarbon on the catalyst, wherein the product eiuent of said hydroformingzone is separated into normally liquid products and a gas. stream, a.substantial portion of said gas stream is branched oii. and recycled tosaid hydroforming zone and the remaining tail-gas portion of said gasstream is supplied to a light ends recovery system, the improvementwhich comprises stripping the catalyst withdrawn from said hydroformingzone in a first stripping zone substantially at said temperatures andpressures with a portion of said recycle gas to remove relatively highboiling volatile combustibles from said catalyst,l withdrawing a mixtureof recycle gasA and relativelyl high boiling combustibles from said rststripping zone, combining said mixture with said product etiluent priorto said separating into normally liquid products and a gas stream,further stripping said stripped catalyst in a separate second strippingzone with, an inert essentially non-combustible stripping gas selectedfrom the group consisting of ue gas and nitrogen to remove relativelylow 4boiling volatile and gaseous combustibles from said catalyst priorto its entry into said regeneration zone, maintaining said catalyst insaid second stripping zone in the form of a dense turbulent solids massfluidized by said inert gas, withdrawing a mixture of said inert gas andremoved low boiling` and gaseous combustibles from said second strippingzone,

8 t and adding said last named mixture to said tail-gas stream at apoint subsequent to the branching off of said recycled portion and.prior to said light ends recovery zone.

lO. The process of claim 9 in which said catalyst has av residence timein said second stripping zone ofv about l-20 minutes.

11. The process of claim 9 in which at least a substantial portion ofsaid gas stream prior to said branchingoii of said recycled gas isfurther separated at a pressure of about 200-500 p. s. i. g. intoproducts liquid at said last-named pressure at about -100 F. and asecondary gas stream, said recycled gas being branched oi said secondarygas stream and the remainder of said secondary gas stream being passedas the tail-gas to said light ends recovery zone.

l2. In the process of continuously hydroforming naphthas in the presenceof a fluidized hydroforming catalyst circulating between a huid-typehydroforming zone and a iiuid-type catalyst regeneration zone for thecombustion of carbon on the catalyst, wherein the product efliuent ofsaid liydroforming zone is subjected to a separation into liquidproducts and a gas stream, a substantial portion of said gas stream isbranched oft" and recycled to said ,hydroforming zone and the remainingtail-gas portion of said gas stream is supplied to a light ends recoveryzone, the improvement which comprises carrying out at least a portion ofsaid separation at an elevated pressure to condense substantial amountsof normally vaporous hydrocarbon products and to render said gas streamrelatively rich in hydrogen and relatively lean in hydrocarbons,Istripping said catalyst circulating from said hydroforming zone to. saidregeneration zone in a separate stripping zone with an inert essentiallynon-combustible stripping, gas selected from the` group consisting of uegas and nitrogen to remove volatile and gaseous combustibles from saidcatalyst prior to its entry into said regeneration zone, withdrawing amixture of said inert stripping gas and volatile gaseous combustiblesfrom said stripping zone and adding said mixture to said tail-gas streamat a point subsequent to the branching-off of said recycled portion andprior to said light ends recovery zone.

References Cited in the iile of this patent UNITED STATES PATENTS NumberName Date 2,409,353 Giuliani et al Oct. 15, 1946 2,419,323 Meinert etal. Apr. 22, 1947 2,421,677 Belchetz June 3, 1947 2,422,262 Russell June17, 1947 2,451,343 Ogorzaly et al. Feb. 8, 1949 2,477,740 Grote Aug. 2,1949 2,487,132 Hemminger Nov. 8, 1949

1. IN THE PROCESS OF CONTINUOUSLY HYDROFORMING NAPHTHAS IN THE PRESENCEOF A FLUIDIZED HYDROFORMING CATALYST CIRCULATING BETWEEN A FLUID-TYPEHYDROFORMING ZONE AND A FLUID TYPE CATALYST REGENERATION ZONE FOR THECOMBUSTION OF CARBON ON THE CATALYST, WHEREIN THE PRODUCT EFFLUENT OFSAID HYDROFORMING ZONE IS SEPARATED INTO NORMALLY LIQUID PRODUCTS AND AGAS STREAM, A SUBSTANTIAL PORTION OF SAID GAS STREAM IS BRANCHED OFF ANDRECYCLED TO SAID HYDROFORMING ZONE AND THE REMAINING TAIL-GAS PORTION OFSAID GAS STREAM IS SUPPLIED TO A LIGHT ENDS RECOVERY ZONE, THEIMPROVEMENT WHICH COMPRISES STRIPPING SAID CATALYST CIRCULATING FROMSAID HYDROFORMING ZONE TO SAID REGENERATING ZONE IN A SEPARATE STRIPPINGZONE WITH AN INERT ESSENTIALLY NON-COMBUSTIBLE STRIPPING GAS SELECTEDFROM THE GROUP CONSISTING OF FLUE GAS AND NITROGEN TO REMOVE VOLATILEAND GASEOUS COMBUSTIBLES FROM SAID CATALYST PRIOR TO ITS ENTRY INTO SAIDREGENERATION ZONE, WITHDRAWING A MIXTURE OF SAID INERT STRIPPING GAS ANDVOLATILE COMBUSTIBLES FROM SAID STRIPPING ZONE AND ADDING SAID MIXTURETO SAID TAIL-GAS STREAM AT A POINT SUBSEQUENT TO THE BRANCHING-OFF OFSAID RECYCLED GAS PORTION AND PRIOR TO SAID LIGHT ENDS RECOVERY ZONE,WHEREBY SAID RECYCLED GAS STREAM AND SAID HYDROFORMING ZONE ARE KEPTENTIRELY FREE OF SAID INERT STRIPPING GAS.